Intramedullary nail

ABSTRACT

The present invention provides an intramedullary nail having a body with a transverse bore extending through the body and having an area of enhanced stress distribution on at least the lateral side of the transverse bore. In one exemplary embodiment, the intramedullary nail includes a cutout adjacent to the transverse bore, such as an oblique cutout, that enhances the stress distribution of the intramedullary nail in the region around the lateral opening of the transverse bore. In one exemplary embodiment, the cutout includes a ramp portion or area that defines the lateral opening of the transverse bore. In other exemplary embodiments, the cutout includes a runout or a substantially flat portion that defines the lateral opening of the transverse bore.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/578,038, filed on Oct. 13, 2009, which claims the benefit under Title35, U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No.61/105,583, entitled STRENGTHENED INTRAMEDULLARY NAIL, filed on Oct. 15,2008, the disclosures of which are expressly incorporated herein byreference in their entireties.

BACKGROUND

1. Field of the Invention

The present invention relates to orthopedic components, and,particularly, to intramedullary nails.

2. Description of the Related Art

Intramedullary nails may be used to align and stabilize fractures of along bone, such as a femur. In a fractured femur, an intramedullary nailmay be inserted into the intramedullary canal of the femur andpositioned to extend across the fracture line of the femur. Then, screwsor other securement devices may be inserted through bores formed in theintramedullary nail on opposing sides of the fractured femur to securethe opposing portions of the fractured femur together.

If the head and/or neck of a long bone, such as the head and/or neck ofthe femur, has fractured, a lag screw may be inserted into a transversebore formed in the intramedullary nail. This bore is aligned so that thelag screw extends through the neck and into the head of the long boneand across the fracture line, allowing the lag screw to reduce thefracture of the neck and/or head of the long bone.

For example, referring to FIG. 1, femur 10 is shown including shaft 12,neck 14, and head 16. As shown, neck 14 of femur 10 has been fracturedat line 17. Transverse bore 18 extends through intramedullary nail 20and is sized to receive lag screw 22 therethrough. Specifically, lagscrew 22 has an outer diameter that is slightly smaller than thediameter of transverse bore 18. This allows lag screw 22 to pass throughtransverse bore 18 and reduce the fracture at line 17.

However, due to the need for lag screw 22 to have an outer diameter thatis less than the diameter of transverse bore 18, lag screw 22 will pivotslightly within transverse bore 18 of intramedullary nail 20 when aforce is applied to the end of lag screw 22. For example, force FG maybe exerted on the end of lag screw 22, which results from head 16 offemur 10 bearing the weight of an individual. When force FG is appliedto the end of lag screw 22, lag screw 22 pivots slightly withintransverse bore 18 of intramedullary nail 20 to create two supportpoints that bear the resultant forces. First support point 24 is amedial, distal support point, where force FM acts on lag screw 22, andsecond support point 26 is a lateral, proximal support point, whereforce FL acts on lag screw 22. By exerting a force on first and secondsupport points 22, 24, force FM induces a compressive stress in the massof the lower part of intramedullary nail 20, while force FL induces atensile stress in the region of transverse bore 18. Additionally, forceFL acting on support point 26 is amplified by the leverage ratio of lagscrew 22 within transverse bore 18. The resulting, theoretical stressdistribution is shown in FIG. 3, where the stress is concentrated aroundthe medial and lateral openings of transverse bore 18.

Referring to FIG. 2, which shows a cross-section of intramedullary nail20, the maximum tension caused by force FL is found near the lateralopening of transverse bore 18, which has sharp edges 27 that are formedin a region with very critical geometry. In addition to the maximumtension occurring at the lateral most side of intramedullary nail 10,the formation of transverse bore 18 in intramedullary nail 20 creates anotch effect that further concentrates stress along sharp edges 27 ofthe lateral opening of transverse bore 18, where a minimal amount ofmaterial is provided. Specifically, the region about the lateral openingof transverse bore 18, for example, has a minimal amount of materialpositioned thereabove as a result of the shape of intramedullary nail20. Stated another way, because intramedullary nail 20 has asubstantially circular cross-section in a direction perpendicular to thelongitudinal axis of intramedullary nail 20 and because the lateralopening to transverse bore 18 is located at an outer edge ofintramedullary nail 20, a minimal amount of material is provided in theregion of support point 26 and the lateral opening of transverse bore18, as compared to the amount of material in the region closer to thelongitudinal axis of intramedullary nail 20. As a result of having aminimal amount of material in the region of the lateral opening oftransverse bore 18, the material in the region of the lateral opening oftransverse bore 18 has a greater concentration of stress than thematerial that is closer to the longitudinal axis of intramedullary nail20. This requires that intramedullary nail 20 is formed from stronger,more expensive materials in order to withstand the increasedconcentration of stress in the material adjacent to the lateral openingof transverse bore 18 and/or has an increased size in the region ofintramedullary nail 20 near the lateral opening of transverse bore 18 inorder to increase the volume of material present and to decrease theconcentration of stress adjacent to the lateral opening of transversebore 18.

SUMMARY

The present invention provides an intramedullary nail having a body witha transverse bore extending through the body and having an area ofenhanced stress distribution on at least the lateral side of thetransverse bore. In one exemplary embodiment, the intramedullary nailincludes a cutout adjacent to the transverse bore, such as an obliquecutout, that enhances the stress distribution of the intramedullary nailin the region around the lateral opening of the transverse bore. In oneexemplary embodiment, the cutout includes a ramp portion or area thatdefines the lateral opening of the transverse bore. In other exemplaryembodiments, the ramp portion of the cutout defines a runout or asubstantially flat portion that defines the lateral opening of thetransverse bore.

Specifically, in forming a cutout adjacent to a transverse bore of anintramedullary nail in accordance with the teachings of the presentinvention, as set forth in detail below, material positioned on thedistal side of the transverse bore and/or adjacent to the lateralopening of the transverse bore is removed. However, the materialpositioned on the proximal side of the transverse bore is maintained.For example, as compared to traditional intramedullary nails having asubstantially cylindrical shape in the area adjacent to the transversebore, material is absence in the present intramedullary nail in the areadirectly distal of and/or adjacent to a lateral opening of thetransverse bore. By creating an absence of material distal of thetransverse bore, the stresses induced at the lateral opening of theintramedullary nail, such as in the area distal of lateral support point54 (FIG. 4A), are distributed in a direction toward the longitudinalaxis of the intramedullary nail. As a result, the stresses introduced atthe lateral support point are distributed through a different portion ofthe intramedullary nail, i.e., through a portion of the intramedullarynail spaced a decreased lateral distance from the longitudinal axis ofthe intramedullary nail relative to the material directly adjacent tothe lateral opening of the transverse bore. This allows for theconcentration of the stress at the lateral support point adjacent to thelateral opening of the transverse bore to be decreased, as the stress isborne throughout the body of the intramedullary nail.

In each of the exemplary embodiments of the present invention, thecutout formed in the intramedullary nail lacks a sharp edge at thedistal end thereof. Instead, each embodiment of the present inventionutilizes a smooth transition zone at the distal end of the cutout. Asindicated above, in one exemplary embodiment, the smooth transition zoneis formed in the distal portion of the cutout as a runout extendingparallel to the axis of the intramedullary nail and terminating at anintermediate portion of the intramedullary nail. In another exemplaryembodiment, the distal portion of the cutout forms an oblique surfacethat terminates distally at the outer surface of a proximal portion ofthe intramedullary nail and forms an angle with the longitudinal axis ofthe intramedullary nail. By altering the angle that the oblique, distalsurface portion of the cutout forms with the longitudinal axis of theintramedullary nail, the specific stress transfer properties of theintramedullary nail may be correspondingly modified and/or optimized fora particular application.

Further, by replacing a sharp edge at the distal end of the cutout witha smooth transition zone, a portion of the intramedullary nail that issubjected to high, oscillating tensile stresses is removed.Additionally, the intramedullary nail may be readily removed from apatient's body, even if bone ingrowth has occurred in the area of thecutout. Specifically, if cancellous bone tissue grows into the areadefined by the cutout, when the intramedullary nail is removed, thesurface defining the distal portion of the cutout may temporarilydisplace the elastic cancellous bone tissue and allow the intramedullarynail to slide smoothly along the displaced bone. Then, once theintramedullary nail is removed, the bone tissue may extend back into thespace within the intramedullary canal previously occupied by theintramedullary nail. As a result, trauma to the bone tissue issubstantially lessened if the intramedullary nail is removed.

Throughout the present application various positional terms, such asdistal, proximal, medial, lateral, anterior, and posterior, will be usedin the customary manner when referring to the human anatomy. Morespecifically, “distal” refers to the area away from the point ofattachment to the body, while “proximal” refers to the area near thepoint of attachment the body. For example, the proximal femur refers tothe portion of the femur near the hip, while the distal femur refers tothe portion of the femur near the tibia. The terms “medial” and“lateral” are also essentially opposites, where “medial” refers tosomething situated closer to the middle of the body, while “lateral”refers to something situated closer to the left side or the right sideof the body (rather than to the middle of the body). With regard toanterior and posterior, “anterior” refers to something situated closerto the front of the body and “posterior” refers to something situatedcloser to the rear of the body. Additionally, when anatomical terms areused with specific reference to an orthopedic implant, such as anintramedullary nail, the terms are used with respect to the implantbeing positioned as intended within the human body, which is shown inthe various drawings of the present application.

In one form thereof, the present invention provides an intramedullarynail, including an elongate body including a proximal end, a distal end,a medial side, a lateral side, and a longitudinal axis. The elongatebody defines an elongate body periphery. The proximal portion of theelongate body has an interior wall defining a transverse bore extendingtherethrough. The transverse bore extends from the lateral side to themedial side of the elongate body in a direction transverse to thelongitudinal axis of the elongate body. The proximal portion includes acutout positioned adjacent to the transverse bore on the lateral side ofthe elongate body. The cutout includes a ledge portion extending in asubstantially medial-lateral direction and positioned adjacent to aproximal most edge of the wall defining the transverse bore. The cutoutalso includes a ramp portion defining a substantially planar surface.The ramp portion forms a ramp angle with the longitudinal axis of theelongate body. The ramp angle is between zero degree and thirty degrees,wherein the ramp portion extends along the longitudinal axis of theelongate body in a distal direction. The ramp portion terminatingdistally at the elongate body periphery, wherein the ramp portionterminates at a position spaced distally from a distal most edge of thewall defining the transverse bore. The cutout also includes anintermediate portion positioned between the ledge portion and the rampportion. The intermediate portion has an intermediate portion radius ofcurvature.

In another form thereof, the present invention provides anintramedullary nail including an elongate body having a proximal end, adistal end, a medial side, a lateral side, and a longitudinal axis. Theelongate body includes a distal portion defining the distal end of theelongate body and a transition portion extending proximally from thedistal portion along the longitudinal axis. The transition portion has aproximal end having a proximal diameter and a distal end having a distaldiameter. The proximal diameter is greater than the distal diameter. Thetransition portion defines a transition portion periphery. The elongatebody also includes a proximal portion extending proximally from thetransition portion and defining a proximal end of the elongate body. Theproximal portion defines a proximal portion periphery. The proximalportion has a diameter substantially equal to the proximal diameter ofthe transition portion. The proximal portion has an interior walldefining a transverse bore extending therethrough. The transverse boreextends from the lateral side of the elongate body to the medial side ofthe elongate body in a direction transverse to the longitudinal axis ofthe elongate body. The proximal portion has a cutout positioned adjacentto the transverse bore on the lateral side of the elongate body. Thecutout defines a derivation from the proximal portion periphery and thetransition portion periphery having a volume of at least 100 cubicmillimeters.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention itself will be better understood by reference to the followingdescription of an embodiment of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a fragmentary, cross-sectional view of a prior artintramedullary nail positioned within a femur and a lag screw extendingthrough a transverse bore of the intramedullary nail to reduce afracture in the neck of the femur;

FIG. 2 is a cross-sectional view of the intramedullary nail of FIG. 1taken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary, side view of the intramedullary nail of FIG. 1depicting theoretical stress lines extending therethrough that arecreated during loading of the lag screw shown in FIG. 1;

FIG. 4A is a fragmentary, side view of an intramedullary nail of thepresent invention according to one exemplary embodiment;

FIG. 4B is a fragmentary view of the intramedullary nail of FIG. 4Ataken in the direction of line 4B-4B of FIG. 4A;

FIG. 5A is a fragmentary, side view of an intramedullary nail of thepresent invention according to another exemplary embodiment;

FIG. 5B is a fragmentary view of the intramedullary nail of FIG. 5Ataken in the direction of line 5B-5B of FIG. 5A;

FIG. 6A is a fragmentary, side view of an intramedullary nail of thepresent invention according to another exemplary embodiment;

FIG. 6B is a fragmentary view of the intramedullary nail of FIG. 6Ataken in the direction of line 6B-6B of FIG. 6A;

FIG. 7A is a fragmentary, side view of an intramedullary nail of thepresent invention according to another exemplary embodiment; and

FIG. 7B is a fragmentary view of the intramedullary nail of FIG. 7Ataken in the direction of line 7B-7B of FIG. 7A;

FIG. 8 is a cross-sectional view of the intramedullary nail of FIGS. 7Aand 7B positioned within a femur and further depicting fixation screwsand a lag screw; and

FIG. 9 is a front, side view of the intramedullary nail of FIG. 8.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate preferred embodiments of the invention and suchexemplifications are not to be construed as limiting the scope of theinvention in any manner.

DETAILED DESCRIPTION

Referring to FIGS. 8 and 9, intramedullary nail 30 is shown and includescutout 32 of FIGS. 7A and 7B, as described in detail below.Intramedullary nail 30 forms a substantially cylindrical, elongate bodyincluding distal portion 34, transition portion 36, and proximal portion38. In one exemplary embodiment, longitudinal bore 40 extends alonglongitudinal axis LA of intramedullary nail 30. Intramedullary nail 30may be made of a titanium alloy, such as Ti-6Al-4V, or any otherbiocompatible orthopedic material, such as medical grade stainless steelor a cobalt-chromium alloy. Transverse, distal bores 42 extend throughdistal portion 34 of intramedullary nail 30 and receive fixation screws44 therein. Referring to FIG. 8, fixation screws 44 are positioned toextend through transverse bores 42 and are secured to shaft 12 of femur10. Fixation screws 44 function to prevent rotation within and/orremoval of intramedullary nail 30 from intramedullary canal 46 of femur10.

As shown in FIGS. 8 and 9, in addition to bores 42, proximal portion 38of intramedullary nail 30 includes wall 49 defining transverse bore 48through which a lag screw, such as lag screw 50, is positioned.Transverse bore 48 of intramedullary nail 30 is aligned with the axis ofneck 14 of femur 10, such that lag screw 50 may be extended throughtransverse bore 48 and implanted into neck 14 and/or head 16 of femur 10to reduce a fracture in neck 14 and/or head 16 of femur 10. In exemplaryembodiments, intramedullary nail 30 and lag screw 50 may form acollodiaphyseal (“CCD”) angle of approximately 125 degrees, 130 degrees,or 135 degrees. While described herein with specific reference to afemur, intramedullary nail 30 may also be used other long bones, such asa tibia, fibula, radius, ulna, and/or clavicle.

In one exemplary embodiment, proximal portion 38 of intramedullary nail30 defines a proximal end of intramedullary nail 30 and has a proximaldiameter. In one exemplary embodiment, the diameter of proximal portion38 is approximately 15.5 mm. In one exemplary embodiment, proximalportion 38 defines a proximal portion periphery having a substantiallycylindrical shape having a diameter equal to the diameter of proximalportion 38 and extending along proximal length PL of proximal portion38. Referring to FIG. 9, in one exemplary embodiment, distal portion 34defines a distal end of intramedullary nail 30 and has a distaldiameter. In exemplary embodiments, the diameter of distal portion 34 isapproximately between 10 mm and 15 mm. In exemplary embodiments, thediameter of distal portion 34 may be equal to approximately 10 mm, 11.5mm, 13 mm, or 14.5 mm. Transition portion 36 extends between proximalportion 38 and distal portion 34 and provides a substantially conicaltransition section between proximal portion 38 and distal portion 34. Inone exemplary embodiment, transition portion 36 has a distal end havinga diameter substantially equal to the diameter of the proximal mostportion of distal portion 34 and a proximal end having a diametersubstantially equal to the diameter of proximal portion 38. For example,transition portion 36 may have a diameter of approximately 15.5 mm at aproximal end thereof and a diameter of approximately 10 mm at a distalend thereof. In one exemplary embodiment, transition portion 36 definesa transition portion periphery having a substantially conical shape witha proximal diameter equal to the diameter at a proximal end oftransition portion 36 and a distal diameter equal to the diameter at adistal end of transition portion 36 and extending along transitionportion length TL.

Still referring to FIG. 9, in one exemplary embodiment, the proximalportion 38 of intramedullary nail 30 has a proximal length PL ofapproximately 58 mm, transition portion 36 has a transition portionlength TL of approximately 31 mm, and distal portion 34 ofintramedullary nail 30 has a distal portion length DL of betweenapproximately 120 mm and 395 mm. For example, distal portion 34 may havea distal portion length DL as small as approximately 126 mm, 211 mm, 231mm, 251 mm, or 271 mm and as large as approximately 291 mm, 311 mm, 331mm, 351 mm, 371 mm, or 391 mm. By combining the overall lengths PL, TL,DL of the proximal portion 38, transition portion 36, and distal portion34, respectively, the overall length L of intramedullary nail 30 isdetermined. In one exemplary embodiment, intramedullary nail 30 has anoverall length L between approximately 210 mm and approximately 480 mm.For example, intramedullary nail 30 may have a length L as small asapproximately 215 mm, 300 mm, 320 mm, 340 mm, or 360 mm and as large asapproximately 380 mm, 400 mm, 420 mm, 440 mm, 460 mm, or 480 mm. In oneexemplary embodiment, length L is equal to approximately 215 mm.

Referring to transverse bore 48 as shown in FIG. 9, transverse bore 48of the intramedullary nail 30 forms angle λ with longitudinal axis LA ofintramedullary nail 30. In one exemplary embodiment, angle λ is betweenapproximately 48 degrees and 60 degrees. For example, angle λ may beequal to approximately 49 degrees, 54 degrees, or 59 degrees. Referringto longitudinal bore 40, in one exemplary embodiment, longitudinal bore40 has a diameter of approximately 4.8 mm, except in the area ofproximal portion 38 where longitudinal bore 40 may be enlarged toaccommodate a set screw (not shown) and/or other components thatfunction to prevent and/or limit translation of lag screw 50 withintransverse bore 48 of intramedullary nail 30.

As described in detail above with respect to prior art intramedullarynail (FIG. 1), during walking or other movement, a patient's weight maybe transferred to the tip of a lag screw, such as lag screw 50 of FIG.8. As a result, lag screw 50 applies a force to intramedullary nail 30at medial and lateral support points 52, 54, adjacent to medial andlateral openings of transverse bore 48, respectively. In order toenhance the stress distribution of intramedullary nail 30 in thevicinity of support point 52, the lateral side of proximal portion 38 ofintramedullary nail 30 includes a cutout formed therein. As shown inFIGS. 8 and 9, intramedullary nail 30 includes cutout 32, which isdescribed in detail below with respect to FIGS. 7A and 7B. Whiledescribed and depicted herein with the cutout formed on the lateral sideof intramedullary nail 30, the cutout may, in other exemplaryembodiments, be formed on both the lateral and the medial sides ofintramedullary nail 30 adjacent to the lateral and medial openings oftransverse bore 48, respectively.

Additionally, while intramedullary nail 30 is shown as including cutout32, intramedullary nail 30 may include any of the cutout designs setforth herein, including the use of different cutout designs on themedial and lateral sides of intramedullary nail 30. Further, as usedherein, the term “cutout” refers generally to an area of a material inwhich the cross-section of the material deviates from an otherwisesubstantially consistent cross-section, but does not require theindependent removal of the material. Thus, as used herein,intramedullary nail 30 may be cast or otherwise formed to include acutout, even though no machining or manufacturing steps were undertakento remove material from intramedullary nail 30 to form the cutout.Further, the cutouts of the present invention result in the creation ofa deviation in the periphery of proximal portion 38, i.e., the proximalportion periphery described above, and/or the periphery of transitionportion 36, i.e., the transition portion periphery described above. Forexample, the derivation in the periphery of proximal portion 38 andtransition portion 36 from a cylindrical geometry with a 15.5 mmdiameter may be as small as 90 mm³, 95 mm³, 100 mm³, or 105 mm³, and maybe as high as 110 mm³, 115 mm³, 120 mm³, or 125 mm³. In one exemplaryembodiment, the derivation in the periphery of proximal portion 38 andtransition portion 36 from a cylindrical geometry with a 15.5 mmdiameter may be equal to substantially 106 mm³.

In exemplary embodiments, described in detail below, the cutouts of thepresent invention define ramp portions that form oblique surfaces withrespect to the longitudinal axis LA of intramedullary nail 30 or,alternatively, when the ramp portion forms a zero degree angle withlongitudinal axis LA of intramedullary nail 30, define runouts that havea surface extending substantially parallel to longitudinal axis LA ofintramedullary nail 30. As described in detail below with specificreference to cutout 56 and FIGS. 4A and 4B, these ramp portions orrunouts function to reduce the concentration of the stress in the areaof the lateral side of transverse bore 48 that is created by theinteraction of lag screw 50 with intramedullary nail 30. As a result,intramedullary nail 30 has higher safety margins than similarintramedullary nails, such as those shown in FIGS. 1-3, which are formedin a traditional manner without the cutouts of the present invention.

Referring to FIGS. 4A and 4B, cutout 56, which is formed according to anexemplary embodiment of the present invention, is shown in conjunctionwith intramedullary nail 30. Cutout 56 is positioned adjacent to anddefines the lateral opening of transverse bore 48. Cutout 56 includesledge portion 58 and runout portion 60. Runout portion 60 defines asubstantially planar surface that extends in a direction substantiallyparallel to longitudinal axis LA of intramedullary nail 30 and definesflattened sides surfaces 62, 64 on opposing anterior and posterior sidesof transverse bore 48. For example, runout portion 60 may form an angleas small as 1 degree, 2 degrees, or 3 degrees with longitudinal axis LAand as large as 177 degrees, 178 degrees, or 179 degrees withlongitudinal axis LA. In one exemplary embodiment, flattened sidesurfaces 62, 64 have a width W of at least substantially 0.2 mm. Byensuring that width W of flattened side surfaces 62, 64 is at leastsubstantially 0.2 mm, a manufacturing tolerance is provide that helps toensure that flattened side surfaces 62, 64 are properly formed duringthe manufacturing process.

Ledge portion 58 and runout portion 60 are connected to one another byintermediate portion 66 and are separated from one another by angle α.In one exemplary embodiment, intermediate portion 66 has a radius ofcurvature of approximately 3 mm. In one exemplary embodiment, angle α issubstantially equal to 90 degrees. In this embodiment, ledge potion 58is substantially perpendicular to longitudinal axis LA of intramedullarynail 30.

In one exemplary embodiment, runout portion 60 extends alonglongitudinal axis LA of intramedullary nail 30, through transitionportion 36, and terminates at the proximal end of distal portion 34 ofintramedullary nail 30. Specifically, in this embodiment, runout portion60 is substantially coplanar with a plane tangent to a lateral mostportion of distal portion 34 and parallel to longitudinal axis LA ofintramedullary nail 30. In other exemplary embodiments, runout portion60 extends into and terminates within distal portion 34. In theseembodiments, runout portion 60 is not substantially coplanar with aplane tangent to a lateral most portion of distal portion 34, but may besubstantially parallel to longitudinal axis LA of intramedullary nail30. Alternatively, in other exemplary embodiments, runout portion 60terminates within transition portion 36. For example, runout portion 60may terminate at the periphery of transition portion 36 as describedabove with reference to the transition portion periphery. In exemplaryembodiments, in order to alter the position at which runout portion 60terminates distally, i.e., the distal most point of runout portion 60,runout portion 60 is maintained in a plane parallel to longitudinal axisLA of intramedullary nail 30 and is moved closer to or further away fromlongitudinal axis LA of intramedullary nail 30. In one example, therunout portion 60 is spaced from the longitudinal axis LA of theelongate body 30 by a distance at least as great as one-half of thedistal diameter of the transition portion 36. In one example, the runoutportion 60 is spaced from the longitudinal axis LA of the elongate body30 by a distance greater than one-half of the distal diameter of thetransition portion 36 and less than the proximal diameter of thetransition portion 36, wherein the runout portion 60 terminates distallyat the transition portion periphery.

By forming cutout 56 in intramedullary nail 30, material having athickness T is positioned on the proximal side of lag screw 50 betweenrunout portion 60 and the lateral-most surface of intramedullary nail 30positioned proximal of lag screw 50, while a corresponding amount ofmaterial is removed from the distal side of lag screw 50. By removingmaterial distally of lag screw 50, the stresses that are introduced inthe material directly adjacent to the lateral opening of transverse bore48, such as in the area distal of support point 54, and described indetail above, are distributed in a direction toward longitudinal axis LAof intramedullary nail 30. As a result, the stresses introduced in thematerial directly adjacent to the lateral opening of transverse bore 48are distributed through a portion of intramedullary nail 30 where thematerial forming intramedullary nail 30 is thicker, i.e., through aportion of intramedullary nail 30 spaced a decreased lateral distancefrom longitudinal axis LA of intramedullary nail 30 relative to thematerial directly adjacent to the lateral opening of transverse bore 48.This allows for the concentration of the stresses in the area of thelateral opening of transverse bore 48 to be reduced, as the stresses arespread throughout the body of intramedullary nail 30.

As a result, intramedullary nail 30 may have a decreased thicknessrelative to known intramedullary nails while providing substantiallysimilar or improved strength properties as compared to knownintramedullary nails. For example, as indicated above, the diameter ofproximal portion 38 of intramedullary nail 30 may be as small as 15.5mm, while the diameter of a proximal portion of a comparable prior artintramedullary nail is 17 mm. Similarly, the diameter of transverse bore48 of intramedullary nail 30 may be as small as 10.5 mm, while thediameter of the corresponding transverse bore of a comparable prior artintramedullary nail is 12 mm.

In order to further enhance the preferential stress distribution ofintramedullary nail 30 of the present invention, flattened side surfaces62, 64 may be formed on opposing sides of lateral opening 68 oftransverse bore 48 as shown in FIG. 4B and described in detail above.Additionally, in the embodiment shown in FIGS. 4A and 4B, the lateralmost point of ledge portion 58 defines support point 54. As a result,support point 54 is maintained in its relative position even in thepresence of cutout 56.

Referring to FIGS. 5A and 5B, another exemplary embodiment of a cutoutformed in accordance with the teachings of the present invention isshown as cutout 70. Cutout 70 may be utilized with intramedullary nail30 of FIGS. 8 and 9 and like reference numerals have been used torepresent corresponding components therebetween. Referring to FIGS. 5Aand 5B, cutout 70 includes ledge portion 72, intermediate portion 74,longitudinal portion 76, and ramp portion 78. Intermediate portion 74connects ledge portion 72 to longitudinal portion 76. In one exemplaryembodiment, intermediate portion 74 has a radius of curvature ofapproximately 3 mm.

Referring to FIGS. 5A and 5B, longitudinal portion 76 defines asubstantially planar surface extending in a plane that is substantiallyparallel to longitudinal axis LA of intramedullary nail 30. In oneexemplary embodiment, longitudinal portion 76 terminates at a pointnear, but proximal of, the distal most portion of the wall definingtransverse bore 48. Stated another way, longitudinal portion 76terminates before reaching the distal most portion of transverse bore48. In a similar manner as runout portion 78 of cutout 70, longitudinalportion 76 defines flattened side surfaces 80, 82 adjacent to theanterior and posterior sides of transverse bore 48. In one exemplaryembodiment, flattened side surfaces 80, 82 have a width W of at least0.2 mm.

Ramp portion 78 of cutout 70 defines a substantially planar, obliquesurface that extends distally from longitudinal portion 76. Ramp portion78 forms angle β with longitudinal axis LA of intramedullary nail 30.Ramp portion 78 is oriented such that ramp portion 78 angles towardlongitudinal axis LA of intramedullary nail 30 in a proximal directionand away from longitudinal axis LA of intramedullary nail 30 in a distaldirection. In one exemplary embodiment, angle β is less than 45 degrees.In another exemplary embodiment, angle β is less than 30 degrees. Inexemplary embodiments, angle β may be as small as approximately 0.0degree (in which ramp portion 78 forms runout portion 78), 0.5 degree, 1degree, 3 degrees, 5 degrees, or 10 degrees and as large asapproximately 15 degrees, 20 degrees, 25 degrees, or 30 degrees.Additionally, the smaller that angle β is the closer ramp portion 78 isto being parallel to longitudinal axis LA of intramedullary nail 30. Asa result, it is easier to form ramp portion 78 during the manufacturingprocess and the volume of the space provided for bone ingrowth isincreased.

Referring to FIGS. 6A and 6B, another exemplary embodiment of a cutoutformed in accordance with the teachings of the present invention isshown as cutout 84. Cutout 84 is substantially similar to cutout 70 ofFIGS. 5A and 5B and may be utilized with intramedullary nail 30 of FIGS.8 and 9 and like reference numerals have been used to representidentical or substantially identical components therebetween. Incontrast to longitudinal portion 76 of cutout 70, longitudinal portion86 of cutout 84 terminates at a point distal of the distal most portionof transverse bore 48. In another exemplary embodiment, longitudinalportion 86 may terminate at a point that coincides with the distal mostpoint of transverse bore 48.

Referring to FIGS. 7A and 7B, another exemplary embodiment of a cutoutformed in accordance with the teachings of the present invention isshown as cutout 32. Cutout 32 is substantially similar to cutout 70 ofFIGS. 5A and 5B and like reference numerals have been used to identifyidentical or substantially identical components therebetween. Referringto FIGS. 7A and 7B, unlike cutout 70 of FIGS. 5A and 5B, no portion ofcutout 32 is parallel to longitudinal axis LA of intramedullary nail 30and cutout 32 lacks longitudinal portion 76. Thus, ledge portion 92 andramp portion 94 of cutout 32 are connected to one another byintermediate portion 96 and are separated from one another by angle λ.In one exemplary embodiment, angle λ is substantially equal to 90degrees. In one exemplary embodiment, intermediate portion 96 has aradius of curvature of approximately 3 mm. In one exemplary embodiment,ledge portion 92 is also curved. In one exemplary embodiment, ledgeportion 32 has a radius of curvature of approximately 3 mm.

Alternatively, in another exemplary embodiment, ledge portion 92 mayinclude a substantially planar portion. In one exemplary embodiment, aplane containing ledge portion 92 intersects the longitudinal axis oftransverse bore 48 and is substantially perpendicular to longitudinalaxis LA of intramedullary nail 30. Referring now to ramp portion 94,ramp portion 94 defines substantially planar surface 98 that tapers awayfrom the longitudinal axis LA of intramedullary nail 30 in a distaldirection to form angle ε (FIG. 7A) relative to longitudinal axis LA ofintramedullary nail 30. In one exemplary embodiment, angle ε is 9degrees. In another exemplary embodiment, angle ε is 10 degrees. In afurther exemplary embodiment, angle ε is 6 degrees. In exemplaryembodiments, angle ε may be any angle in the range of 4-12 degrees.

In exemplary embodiments, due to angles γ and angles ε (FIG. 7A), ledgeportion 92 may form a slight angle relative to a line that isperpendicular to longitudinal axis LA of intramedullary nail 30. Thus,while ledge portion 92 may still remain substantially perpendicular tolongitudinal axis LA, ledge portion 92 may form an angle δ (FIG. 7A)with longitudinal axis LA of intramedullary nail 30. Thus, in exemplaryembodiments, instead of angle δ being 90 degrees from longitudinal axisLA and ledge portion 92 being perpendicular with longitudinal axis LA,angle δ will, for any particular embodiment, be equal to 180 degreesminus the sum of angle γ and angle ε. For example, when angle γ is 90degrees and angle ε is 10 degrees, angle δ will be equal to 80 degrees.

In order to form any of cutouts 32, 56, 70, 84 in intramedullary nail30, cutouts 32, 56, 70, 84 may be machined into intramedullary nail 30by advancing a cutting tool having a radius substantially equal to thedesired radius of intermediate portion 66, 74, 96 in a directionsubstantially transverse to longitudinal axis LA of intramedullary nail30. In one exemplary embodiment, a longitudinal axis of the cutting toolis aligned perpendicularly to the longitudinal axis of transverse bore48. In one exemplary embodiment, the movement of the cutting tool may beautomatically controlled, such as by the use of a computer numericalcontrol (“CNC”) machine. Once the cutting tool has reached the desireddepth, further movement of the cutting tool into, i.e., in a directiontoward longitudinal axis LA of intramedullary nail 30, is stopped. Byadvancing a cutting tool having a radius of curvature substantiallysimilar to the radius of curvature of intermediate portion 66, 74, 96 tothe desired depth, both ledge portion 58, 72, 92 and intermediateportion 66, 74, 96 are created substantially simultaneously.

Then, in order to form longitudinal portion 76, 86 or runout portion 60,if required, the cutting tool is moved in a distal directionsubstantially parallel with longitudinal axis LA of intramedullary nail30. Once the cutting tool has been advanced to the desired distaltermination point of longitudinal portion 76, 86 or, for runout portion60, out of the material forming intramedullary nail 30, ramp portion 78,90 may be formed. Alternatively, if longitudinal portion 76, 86 is notrequired, such as for cutout 32, the step of forming longitudinalportion 76, 86 is skipped and ramp or runout portion 60, 78, 90 isformed directly after forming ledge portion 58, 72, 92 and intermediateportion 66, 74, 96.

In order to form ramp portion 78, 94, the cutting tool may be advancedfrom the desired depth in both a distal direction and a direction outof, i.e., away from the longitudinal axis LA of, intramedullary nail 30.Stated another way, the cutting tool is advanced away from longitudinalaxis LA along a plane forming angle β, ε (FIGS. 5A, 7A) relative tolongitudinal axis LA. The advancement of the cutting tool in this manneris continued until the cutting tool no longer contacts the materialforming intramedullary nail 30. Once the cutting tool no longer contactsthe material forming intramedullary nail 30, ramp portion 78, 94 isformed.

Alternatively, in another exemplary embodiment, in order to form rampportion 78, 94 and/or longitudinal portion 76, 86, the cutting tool maybe removed from intramedullary nail 30 after forming ledge portion 58,72, 92, intermediate portion 66, 74, 96, and, in some embodiments,longitudinal portion 76, 86 and repositioned at a point that is at thedesired distal most point of the cutout. The cutting tool may beadvanced from this distal point in a direction that is both into, i.e.,toward longitudinal axis LA, and proximal relative to intramedullarynail 30. Stated another way, the cutting tool is advanced towardlongitudinal axis LA along a plane forming angle β, ε 8 (FIGS. 5A, 7A)with longitudinal axis LA. As the cutting tool continues to be advanced,the length and depth of ramp portion 78, 94 is correspondinglyincreased. The advancement of the cutting tool is stopped when thecutting tool is substantially adjacent and/or contacts intermediateportion 66, 74, 96 or a distal most point of longitudinal portion 76,86. Then, if not yet formed, longitudinal portion 76, 86 may be formedby advancing the cutting tool in a proximal direction parallel withlongitudinal axis LA of intramedullary nail 30.

In another exemplary embodiment, cutouts 32, 56 are machined intointramedullary nail 30 by advancing a cutting tool having a radius thatis greater than the desired radius of intermediate portions 96, 66 fromone of an anterior side and a posterior side of intramedullary nail 30to the other of the anterior side and the posterior side ofintramedullary nail 30. Specifically, referring to FIG. 7A and cutout32, a longitudinal axis of the cutting tool is aligned to form angle εwith longitudinal axis LA of intramedullary nail 30. Then, the cuttingtool is positioned at one of the anterior or posterior sides ofintramedullary nail 30 with the tip of the cutting tool advanced to aproximal position equal to the desire proximal most point of ledgeportion 92. The cutting tool is then advanced across the lateral side ofintramedullary nail 30 to the opposing anterior or posterior side andledge portion 92 and ramp portion 94 of cutout 32 are formed.Additionally, by using a standard cylindrical cutting tool, ledgeportion 92 may be formed with angle γ (FIG. 7A) being substantiallyequal to ninety degrees. Once ledge portion 92 and ramp portion 94 areformed, an additional machining step, such as one of the steps describedin detail above, is needed to form intermediate portion 96. In oneexemplary embodiment, the movement of the cutting tool may beautomatically controlled, such as by the use of a computer numericalcontrol (“CNC”) machine. Advantageously, by forming cutouts 32, 56 byusing a cutting tool having a diameter greater than the desired diameterof intermediate portions 96, 66 and by advancing the cutting tool acrossintramedullary nail 30 instead of along the longitudinal axis LA ofintramedullary nail 30, less vibration is generated in intramedullarynail 30 during the formation of cutouts 32, 56.

In other exemplary embodiments, cutouts 32, 56, 70, 84 may be formed inintramedullary nail 30 by casting, forging, or other known manufacturingtechniques.

While this invention has been described as having a preferred design,the present invention can be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains and which fallwithin the limits of the appended claims.

What is claimed is:
 1. An intramedullary nail, comprising: an elongate body including a proximal end defined by a proximal portion, a distal end defined by a distal portion, a medial side, a lateral side, and a longitudinal axis, said elongate body defining an elongate body periphery, said proximal portion of said elongate body having an interior wall defining a transverse bore extending therethrough, said transverse bore extending from said lateral side to said medial side of said elongate body in a direction transverse to said longitudinal axis of said elongate body, said proximal portion including a cutout positioned adjacent to said transverse bore on said lateral side of said elongate body, said cutout comprising: a ledge portion extending in a substantially medial-lateral direction and positioned adjacent to a proximal most edge of said wall defining said transverse bore; a ramp portion defining a substantially planar surface, said ramp portion forming a ramp angle with said longitudinal axis of said elongate body, said ramp angle being between zero degrees and thirty degrees, wherein said ramp portion extends along the longitudinal axis of the elongate body in a distal direction, said ramp portion terminating distally at said elongate body periphery, wherein said ramp portion terminates at a position spaced distally from a distal most edge of said wall defining said transverse bore; and an intermediate portion positioned between said ledge portion and said ramp portion, said intermediate portion having an intermediate portion radius of curvature; wherein said ramp portion defines a runout portion defining a substantially planar surface, said runout portion extending in a plane substantially parallel to both said longitudinal axis of said elongate body and a plane tangent to said elongate body periphery at a lateral point of said proximal portion; and wherein said elongate body further comprises a transition portion extending proximally from said distal portion along said longitudinal axis, said transition portion having a proximal end having a proximal diameter and a distal end having a distal diameter, said proximal diameter being greater than said distal diameter, wherein said runout portion is spaced from said longitudinal axis of said elongate body by a distance greater than one-half of said distal diameter of said transition portion and less than said proximal diameter of said transition portion, wherein said runout portion terminates distally at said transition portion periphery.
 2. The intramedullary nail of claim 1, wherein said cutout further comprises a longitudinal portion extending between said intermediate portion and said ramp portion, said longitudinal portion defining a substantially flat surface extending substantially parallel to said longitudinal axis of said elongate body.
 3. The intramedullary nail of claim 2, wherein said longitudinal portion terminates distally at a position between a proximal most edge of said wall defining said transverse bore and a distal most edge of said wall defining said transverse bore.
 4. The intramedullary nail of claim 2, wherein said longitudinal portion terminates distally at a position spaced distally from a distal most edge of said wall defining said transverse bore.
 5. The intramedullary nail of claim 2, wherein said longitudinal portion defines flattened side surfaces on opposing anterior and posterior sides of said transverse bore, each of said flattened side surfaces having a width of at least substantially two millimeters.
 6. The intramedullary nail of claim 1, wherein at least a portion of said ledge portion is positioned no more proximally than a proximal most portion of said wall defining said transverse bore, wherein said ledge portion defines a lateral support point for a lag screw received within said transverse bore of said elongate body.
 7. The intramedullary nail of claim 1, wherein said ramp portion defines flattened side surfaces on opposing anterior and posterior sides of said transverse bore, each of said flattened side surfaces having a width of at least substantially two millimeters.
 8. The intramedullary nail of claim 1, wherein said ledge portion forms a separation angle with said ramp portion, said separation angle being equal to substantially ninety degrees.
 9. An intramedullary nail, comprising: an elongate body including a proximal end defined by a proximal portion, a distal end defined by a distal portion, a medial side, a lateral side, and a longitudinal axis, said elongate body defining an elongate body periphery, said proximal portion of said elongate body having an interior wall defining a transverse bore extending therethrough, said transverse bore extending from said lateral side to said medial side of said elongate body in a direction transverse to said longitudinal axis of said elongate body, said proximal portion including a cutout positioned adjacent to said transverse bore on said lateral side of said elongate body, said cutout comprising: a ledge portion extending in a substantially medial-lateral direction and positioned adjacent to a proximal most edge of said wall defining said transverse bore; a ramp portion defining a substantially planar surface, said ramp portion forming a ramp angle with said longitudinal axis of said elongate body, said ramp angle being between zero degrees and thirty degrees, wherein said ramp portion extends along the longitudinal axis of the elongate body in a distal direction, said ramp portion terminating distally at said elongate body periphery, wherein said ramp portion terminates at a position spaced distally from a distal most edge of said wall defining said transverse bore; and an intermediate portion positioned between said ledge portion and said ramp portion, said intermediate portion having an intermediate portion radius of curvature, wherein said ramp portion defines a runout portion defining a substantially planar surface, said runout portion extending in a plane substantially parallel to both said longitudinal axis of said elongate body and a plane tangent to said elongate body periphery at a lateral point of said proximal portion, wherein said elongate body further comprises a transition portion extending proximally from said distal portion along said longitudinal axis, said transition portion having a proximal end having a proximal diameter and a distal end having a distal diameter, said proximal diameter being greater than said distal diameter, wherein said runout portion is spaced from said longitudinal axis of said elongate body by a distance at least as great as one-half of said distal diameter of said transition portion, and wherein said distal portion has a distal portion periphery and said runout portion is substantially coplanar with a plane tangent to said distal portion periphery at a proximal most point of said distal portion periphery, whereby said runout portion terminates distally at said distal portion periphery.
 10. The intramedullary nail of claim 9, wherein said ledge portion forms a separation angle with said runout portion, said separation angle being equal to substantially ninety degrees.
 11. The intramedullary nail of claim 9, wherein at least a portion of said ledge portion is positioned no more proximally than a proximal most portion of said wall defining said transverse bore, wherein said ledge portion defines a lateral support point for a lag screw received within said transverse bore of said elongate body.
 12. The intramedullary nail of claim 9, wherein said runout portion defines flattened side surfaces on opposing anterior and posterior sides of said transverse bore, each of said flattened side surfaces have a width of at least substantially two millimeters. 